Particle size selection in capillary instability of locally heated coaxial fiber

Reduced model for capillary breakup with thermal gradients: Predictions and computational validation

“…Linear stability analysis gives accurate predictions for the size of particles produced by isothermal co-axial fibredrawing processes 10 , but it does not predict the droplets in the dynamic thermal-gradient process considered here 2,11 . Simple extensions of linear stability analysis to the thermalgradient case (Fig.…”

“…As a result, the viscosity profile µ i (z) of the inner silicon varies from 6 • 10 −4 to 5 • 10 −4 Pa s, while the viscosity profile µ o (z) of the outer silica varies from 7 • 10 8 to 3 • 10 5 Pa s. Although the viscosity of the inner silicon is not significantly affected by the axial thermal gradient imposed by the flame, the opposite is true for the outer silica, whose viscosity changes by more than three orders of magnitude over millimeter scales. Such a drastic viscosity gradient is believed to be the reason for the dependence on feed speed of the resulting droplet size 2,11 . Finally, the surface tension between silicon and silica is taken to be γ = 10 N/m.…”

“…Because the capillary number scales as the product of feed speed and viscosity, sufficiently high feed speeds cause breakup to occur deeper into the flame, in such a way that the long-wavelength assumption of the reduced model holds. As a result, the reduced model is a useful tool for designing future experiments, since it takes the form of a pair of 1D partial differential equations (PDEs) 11 that are vastly simpler and more efficient to simulate than a full 3D axisymmetric Stokes model. Capillary instability of liquid threads and jets is a widely studied subject.…”

“…Simple extensions of linear stability analysis to the thermalgradient case (Fig. 1) have thus far failed to produce accurate results 11 or require unknown dimensionless fit parameters 2 . This motivated the numerical simulations of the long-wavelength reduced model presented in Ref.…”

From droplets to waves: periodic instability patterns in highly viscous microfluidic flows

“…Microfluidic technologies provide advanced experimental platforms with fine control over flow rates and microgeometries to investigate the role of fluid properties in multiphase flow instabilities (Hu & Cubaud 2018). For liquid-liquid systems, monodisperse droplet dispersions can be steadily generated using microchannels and find use to encapsulate reagents in domains as diverse as material synthesis, drug discovery and the food industry (Barrero & Loscertales 2007;Baroud, Gallaire & Dangla 2010;Anna 2016;Evangelio, Campos-Cortés & Gordillo 2016;Mowlavi et al 2019). Two common regimes of droplet formation have been identified as dripping and jetting based on the location of droplet pinch-off from the fluid junction (Eggers 1997;Guillot et al 2007;Cubaud & Mason 2008;Nunes et al 2013;Gordillo, Sevilla & Campo-Cortés 2014).…”